1. Field of the Invention:
This invention relates to the production of ceramic-grade uranium dioxide powder, and more particularly it pertains to the alternate conversion of uranium hexafluoride to uranium dioxide particles of controlled size by the initial production of seed particles of suitable size of uranium dioxide or intermediate reaction product (uranium oxides and oxyfluorides), for introduction into a fluidized bed reactor where the seed particles serve as substrates on which the deposition of uranium dioxide may be carried out to produce particles of UO.sub.2 of the desired size.
2. Description of the Prior Art:
In a fluidized bed chemical reaction system, such as disclosed in U.S. Pat. No. 3,547,598, gas-phase chemical reactions between uranium hexafluoride, steam and hydrogen are carried out within a fluidized bed of solid particulates and the solid product of the reaction forms as accretions on the fluidized particulates. The solid product, uranium oxide and oxyfluoride particles, is withdrawn either continuously or intermittently from the lower end of the fluidized bed in a first reactor and converted further in a second reactor.
It has become a practice to initiate production in such a system by charging it with an initial starting bed of substrate material of substantially the same enrichment composition as the ultimate reaction product. Usually the substrate material is provided from retained inventory of prior production runs, or by providing an inert substrate and rejecting the product produced in the early portion of a production period until the inert bearing substrate has been purged from the system. Both of these procedures incur economic penalties. Moreover, prior attempts to generate the necessary substrate in the reactor by gas-phase reaction without an initial starting bed have failed because the gas-phase reaction without the presence of a substrate yields a solid product of a small particle size which is lost from the reactor by elutriation, or if retained, fails to have adequate fluidization characteristics.